I upgraded my samba ADDC, fileserver and all the winbind-clients a few weeks ago and didn't run into any problems.
edit: Of course, don't rely on a single success message (and to make matters more complicated, I'm also building/running it with libressl and MIT krb5 instead of the default, openssl and heimdal from base). You're on ZFS, so take a snapshot before upgrading (if running on bare metal, a boot environment is helpful!), so you have a simple rollback plan in case anything goes wrong. That's what I did when I upgraded....
